9/12 Brainstem3 - Rasin Flashcards
dorsal structures of pons
- facial colliculus (ventral aspect of 4th ventricle - choroid plexus-less; CP only found in part adj to medulla)
- hypoglossal trygone
- 3x cerebellar peduncles
relationship between pontine nuclei and cerebellar peduncles
transverse section : see large middle cerebellar peduncles made of axons and pontine nuclei
- axons of cells in pontine nuclei make up contralateral middle cerebellar peduncle!
conduit function of pons
descending pathways
- corticospinal/corticobulbar pathways
- anterior corticospinal pathway
ascending pathways
- DCMLS
- spinothalamic tract
CN V
sensory/motor components
trigeminal nerve
both motor (tiny efferent)/sensory (huge afferent) components
sensory components of CN V
1. GSA (general somatic afferent) from face for
- face x 3!!!
- pain and temp
- touch/pressure/conscious propriop.
- subconscious propriop.
- touch and pain for nasal sinuses, inside nose, inside mouth (oronasal mucous membranes/teeth), ant. 2/3 tongue
- pain for supratentoria dura mater (ant. part)
motor components of CN V
1. SVE (special visceral efferent) : muscles from branchial arches
- muscles of mastication
- tensor tympani m.
peripheral branches of CN V
CN V has 3 peripheral branches
- V1 opthalmic division
- V2 maxillary division (incl upper teeth)
- V3 mandibular division (incl lower teeth)
nuclei of CN V
CN V has 4 nuclei (3 sensory, 1 motor)
1. spinal trigeminal nucleus : pain/temp
- extends from pons through medulla to cervical levels (3 levels!)
2. chief/principal sensory nucleus : touch/pressure
- pons only
3. mesencephalic nucleus : subconscious proprioception
- extends from pons into mesencephalon
4. motor nucleus of V : muscles of mastication
trigemino-thalamic pathway
pain, temp, some touch
1st order neuron : trigeminal ganglion
- descends and synapses on spinal nucleus
2nd order neuron : spinal nucleus of V (medulla)
- decussation occurs at levels of pons and medulla (due to extended nature of nucleus) → cross to form trigeminothalamic fibers
3rd order neuron : VPM nucleus of thalamus
spinal trigeminal tract and nucleus
ipsi or contra?
where does decussation occur?
location/length
spinal nucleus carries GSA which conduct ipsilateral impulses of pain, temp, and some touch from head face and neck
- ipsilat because decussation occurs when second order neurons cross over to contralat side on way to VPM of thalamus (AFTER they synapse at spinal nuc)
location: lateral to cuneate tract/nucleus
- spinal tract superficial, spinal nucleus deep
extends form lower pons to upper cervical segments (C2-C3)
which artery affects pain and temp for face?
PICA!!!!
lateral medullary syndrome
- would lose pain/temp sensation on ipsilateral face
spatiotemporal maps of spinal trigeminal nucleus
imagine taking widening ice cream scoops out of the face
- scoop1 = nose/lips
- scoop2 = eye/chin
- scoop3 = top 2/3 of head/top of ear/chin
- scoop4 = middle of ext surface
within the spinal trigeminal nucleus, there is a column of cells each for V1, V2, V3, VII/IX/X (ventral → dorsal arrangement)
- the scoops are arranged 1-4 in a ventral→dorsal arrangement in each column!
what nerves (aside from V) contribute to the spinal trigeminal nucleus???
IX : sensation for back of ear, posterior 1/3 of tongue, upper pharynx (along with X/gagreflex)
- this is how pain/temp for both ant 2/3 (V) and post 1/3 (IX) end up in the same place!
X : sensation for pharynx, larynx, ext ear and dura of post fossa
VII : GSA from back of outer ear
trigemino-lemniscal pathway
touch, pressure (vibration/proprioception)
1st order neuron : trigeminal ganglion
- stays level and synapses on chief/principal trigeminal/sensory nucleus
2nd order neuron : principal sensory nucleus of V (pons)
- decussation occurs at levels of pons → cross to form trigeminal lemniscus
3rd order neuron : VPM nucleus of thalamus
location of principal sensory nucleus
posterior to CST and pontine nuclei, slightly more lateral on dorsal side
mesencephalic nucleus of V
what is received?
what is the function?
where is it located?
unconscious proprioception & “jaw jerk reflex”
**ONLY NUCLEUS THAT CONTAINS PRIMARY SENSORY AFFERENTS**
- jaw jerk reflex allowed for by connection of primary sensory afferents → motor nucleus of V
fx : controls the force of bite, conveys proprioceptive and pressure impulses from face
- teeth, peridontium, hard palate, muscles of mastication, joint capsule via muscle spindles and other mechanoreceptors
location: below superior cerebellar peduncles,
motor nucleus of V
innervates SVE : muscles of mastication and tensor tympani
- located slightly more medially (motor!)
summary for nuclei of V
everything ipsilateral!
- crossing occurs at neurons that project from the nuclei on up to thalamus/cortex
CN V lesions
- trigeminal neuralgia
- causes of sensory loss to face
- atrophy of affected side
- deviation of jaw to affected side on opening (due to pterygoid muscles that draw mandible forward/midline)
- loss of corneal/jaw jerk reflex
trigeminal neuralgia (Tic doloureux)
- recurrent episodes of brief severe pain lasting from seconds to mins (V2-V3)
- normal facial sensation
- mostly unknown cause
sensory loss of face
- trauma
- metastatic disease
- trigem/vestibular Schwannoma
- meninioma
- demyelination
- aneurysom of petrous portion of ICA
- infarcts
- herpes zoster
CN VII
components
facial nerve
carries both motor and sensory components
- involves multiple brainstem nuclei, but axons come together to form a single nerve at level of pontomedullary jx
2 efferent motor components
1. SVE (special visceral efferent) for muscles from branchial arches…
- muscles of facial expression, stapedius, part of digastric m.
2. GVE (general visceral efferent) to pregang PSNS to…
- saliv/lacrim-ation : lacrimal, sublingual, submandibular, all other salivary glands (EXCEPT parotid - IX)
3 afferent sensory components
1. GSA (general somatic afferent) : sensation from small region near outer ear
2. SVA (special visceral afferent) : taste from ant 2/3 tongue
3. GVA (general visceral afferent) : some nasopharynx mucous membrane
nuclei of VII
- motor nucleus of VII : SVE (muscles derived from branchial arches)
- superior salivatory nucleus : GVE (PSNS to salivary/lacrimation)
- rostral solitary nucleus : SVA (taste to ant 2/3 tongue)
honorable mention: spinal nucleus of V!
- GSA from back of outer ear (along with IX and X)
- crosses and ascends in trigeminothalamic tract to VPM_thalamus
nucleus involved with CN VII motor fx
facial motor nucleus
location/structures associated
what is innervated?
facial motor nucleus
- gives off axons that will loop around the abducens nucleus and form facial colliculus (bulging out of floor of 4th ventricle) in process
innervates. .. - muscles of facial expression
- stapedius
- digastric
need-to-know re: corticobulbar projection to motor nucleus of VII
UMNs from both ipsilat and contralat cortex synapse on LMN to upper face → bilat innervation
HOWEVER
ONLY UMN from contralat cortex synapse on LMN to lower face → contralat innervation only
implication: LESION THAT KNOCKS OUT UMN of one side will affect contralateral lower face!
- will be able to move eyebrows, but not able to smile on one side
reflexes involving motor nucleus of CN VII
- corneal → opthlamic nerve CN V (orbicularis oculi)
- sucking → mandibular nerve CN V (orbicularis oris)
- blinking_light → optic nerve CN II (orbicularis oculi)
- blinking_noise → cochlear nucleus CN VIII (orbicularis oculi)
- sound attenuation → cochlear nucleus (stapedius)
nucleus involved with CN VII motor function
superior salivatory nucleus
what’s innervated?
GVE : pregang PSNS to lacrimal, nasal mucosa, submandibular/sublingual salivary glands
nucleus involved with CN VII taste
rostral solitary nucleus
SVA (special visceral afferent) carrying taste from ant 2/3 of tongue
CN VII lesions
Bell’s palsy
- acute, overnight unilateral facial weakness (LMN)
- retroauricular pain
- hyperacusis (sometimes)
- dry eye (sometimes)
- loss of taste (sometimes)
pons summary : locations of nuclei map
vascular supply of pons
anterior circ : internal carotid artery
posterior circ : vertebral artery
basilar a. → paramedian branches will cover pons midline structures
- CST, pontine nuclei, abducens nucleus
AICA and SCA → circumferential branches/lateral pontine aa. will cover pons lateral structures
- facial nucleus, sensory nucleus of V, motor nucleus of V, and DESCENDING SYMPATHETIC FIBERS!!!!
- sympathetic issues : Horner’s syndrome →
- PSNS prevailing (miosis, ptosis, enopthalmose - sinking of eye)
- low SNS (anhidrosis, hi skin temp, flushing of skin)
- sympathetic issues : Horner’s syndrome →
dorsal view of midbrain
exit of CN IV
- only CN to exit dorsally
4 bulbs (2 superior colliculi, 2 inferior colliculi) → “quadrigeminal”
- SC associated with visual pathways
- IF associated with auditory pathways
- “eyes above ears”
both colliculi connected to diencephalon; cross midbrain-diencephalic jx via…
- bSC (brachium superior colliculus)
- bIC (brachium inferior colliculus)
cerebral peduncles
CST and corticobulbar tract descend from internal capsule through cerebral peduncles
- somatotopic organization: leg lateral, trunk middle, arm medial, face even more medial
corticopontine fibers descending to reach pontine nuclei to form the plan (“what do you want to do?”)
lateral & anterior corticospinal pathways
control of fine movement
1st order : layer V cells of motor cortex (upper)
2nd order : ventral horn laminae VII, VIII, IX
3rd order : motor neurons of layer IX (lower)
- lateral CST decussates in medulla
- anterior CST crosses at spinal segmental layers
- BOTH display somatotopic org
descending pathways of midbrain
tracts (location?)
what do they control?
where do they decussate and descend?
- red nucleus (RN) aka “nucleus ruber” → rubrospinal tract
- location of RN: behind cerebral peduncles and substantia nigra
- control of contralateral extremities’ movement, esp FLEXORS
- decussates in midbrain (ventral tegmental decussation) → contralateral rubrospinal tract
rubrospinal tract ends up descending in lateral column (v close to lat CST) → terminates at cervical levels
- tectospinal tracts
- location: originates in superior colliculus of midbrain
- controls coordination of head and eye movement
- decussates in midbrain
ends up descending in anterior spinal cord → terminates at cervical levels
summary of lateral and medial descending motor systems
rubrospinal tract ends up in lateral motor system
tectospinal tract ends up in medial motor system
ascending pathways of midbrain
relation of two ascending pathways as you move up
implication for midbrain lesions
recall: when ascending, DCMLS and spinothalamic/anterolateral systems are…
- far apart in spinal cord
- far apart in medulla
- closer together in pons
- together in midbrain
implication: lesion affecting midbrain → all sensory modalities of contralateral side will be affected!
nuclei of CN III
nucleus of CN III : motor is medial to sensory
- superior to nucleus of CN IV
- comprised of oculomotor nuclei & Westphal-Edinger nucleus
- contains GSE and GVE (Westphal-Edinger nucleus : PSNS fibers → miosis in Horner’s syndrome)
nucleus of CN IV
trochlear nucleus
- inferior to motor nucleus of CN III (medial)
- contains GSE → superior oblique m.
- cross to contralateral side and exit on dorsal side
nucleus of VI
NOT IN MIDBRAIN!!!
- abducens nucleus in pons (surrounded by axons that comprise the facial colliculus!)
- exits in midline at pontomedullary jx
vascular supply of midbrain
which artery? why is it critical?
general coverage zones and arteries associated
posterior cerebral arteries → cerebral peduncles
- lesions here have severe effects: all the tracts are jammed up close to one another in the midbrain!
- motor: CST & CBT
- all sensories (antlat, ML, trigeminal pathways all together)
COVERAGE
proximal PCA → cerebral peduncles, substantia nigra, sensory pathways, descending sympathetic fibers
paramedian branches at top of basilar artery → caudal portion of midbrain (medial)
SCA & prox PCA → posterior portion of midbrain
